Dorsal column stimulation is an established technology for management of chronic low back and leg pain when other surgical options have failed or are not feasible. Conventional dorsal column stimulation systems treat chronic pain by providing electrical stimulation pulses through an electrode array placed in the epidural space next to a patient's spinal cord. The stimulation parameter set determines the characteristics of the stimulation pulses provided through the electrode array in conjunction with the electrodes used to provide the stimulation pulses. Typically, the optimal stimulation parameter set for a specific patient can be determined from the response of the patient to various sets of stimulation parameters.
A dorsal column stimulation system typically includes an implantable pulse generator (IPG), an electrode array, an electrode lead, and an electrode lead extension. Conventionally, the electrodes are implanted against the outer surface of the dura, which is a membrane that surrounds the spinal cord. In operation, the IPG generates electrical pulses that are delivered, via the implanted electrodes, to the dorsal column and dorsal root fibers within the spinal cord. In one aspect, the electrodes are typically arranged and spaced in a desired pattern to create an electrode array and individual wires within one or more electrode leads are connected with each electrode in the array. The electrode leads exit the spinal column and can be attached to one or more electrode lead extensions, which, in turn, are typically tunneled subcutaneously around the torso of the patient to a subcutaneous pocket where the IPG is implanted.
In order for dorsal column stimulation to be effective, the electrodes should be placed in a location such that the electrical stimulation will affect the targeted nerves and cause paresthesia (a feeling of tingling or numbness). The paresthesia perceived by the patient and induced by the stimulation should ideally be located in approximately the same place in the patient's body as the pain that is the target of treatment. If one or more electrodes in the electrode array are not correctly positioned, it is possible that the patient will receive little or no benefit from an implanted dorsal column stimulation system. Thus, correct electrode placement can mean the difference between effective and ineffective pain therapy.
However, precise placement of an electrode relative to the patient's distribution of pain can be difficult due to anatomic variations among patients and due to the inherent limitations of standard electrode designs. Conventionally, electrodes are made of flexible plastic and are inserted into the epidural space through an opening created by a laminotomy procedure that involves the removal of the posterior aspect of a vertebra, which normally forms the spinal canal and protects the spinal cord. Typically, because the electrode is pushed into position by its tail, the electrode will generally follow the path of least resistance, which often results in suboptimal or undesired placement of the electrode with respect to the stimulation target. It is also known that the patient's anatomy can cause deflection of the electrode during the electrode insertion process, thereby making midline electrode placement difficult to achieve. Even a perfect midline placement, as judged by flouroscopy, can result in unilateral stimulation rather than bilateral stimulation of the spinal cord. This problem can prevent optimal electrode placement and, consequently, limit the pain relief experienced by the patient.
There are several known options for overcoming the problems associated with electrode placement; however, each option has significant limitations. One conventional option is the use of a percutaneous cylindrical electrode. These electrodes are typically introduced through a needle and have an internal (coaxial) guidewire that can be contoured to assist with accurate placement. While percutaneous electrodes are well suited for ambulatory trial purposes, these electrodes are not reliable for long-term uses. Specifically, the round, thin designs of percutaneous electrodes make them vulnerable to migration and pullout. Additionally, percutaneous electrodes have compact electrode contact arrays that limit their stimulation distribution. Further, percutaneous electrodes rapidly consume their batteries as energy is expended radially from the electrode contacts rather being exclusively directed toward the spinal cord.
Another conventional option for overcoming the problems associated with electrode placement is the use of paddle-style electrodes, which cover a larger surface area and have an extensive contact array that allows for flexibility with programming stimulation parameters. Paddle-style electrodes are also likely to be relatively stable once post-operative scarring occurs. However, it is difficult to adjust the positioning of paddle-style electrodes without more extensive surgical procedures. Conventionally, an extensive laminectomy can be used to expose the entire site for planned electrode coverage. This requires a larger incision and more muscle manipulation that can add time and morbidity to the procedure. Alternatively, a separate laminotomy superior to a first laminotomy can be utilized (either through the same or a second incision) to visualize and adjust the electrode. This too requires a larger incision and muscle manipulation.
Accordingly, there is a need in the pertinent art for systems and methods of dorsal column stimulation that allow for precise, efficient, and stable placement and repositioning of stimulating electrodes while requiring only a single small incision. There is a further need for systems and methods of dorsal column stimulation that allow for precise, efficient, and stable placement and repositioning of stimulating electrodes through restriction of the contouring of the stimulating electrodes during implantation. There is a further need for systems and methods of dorsal column stimulation that allow for precise, efficient, and stable placement and repositioning of stimulating electrodes using through the use of stimulating electrodes that are configured to promote the formation of a desired insertion pathway within the body of the subject.